In 3GPP (Third Generation Partnership Project), it has been agreed that downlink multiantenna transmission for the long term evolution LTE of 3GPP (sometimes termed 3.9G) supports up to two codewords (CW) or streams (a stream can be as little as a single data codeword on the downlink shared channel), so that a downlink shared channel transmission to the user equipment UE in a multi-antenna system (e.g., four antennas each at the base station BS and the user equipment UE) may use two different transmission formats, one for each DL shared channel codeword. The used shared channel transmission formats used on all shared channel codewords transmitted to the UE need to be indicated to the UE, typically on a control channel. This can be interpreted in the way that there are multiple codewords transmitted on the control channel, one for each of the shared channel codewords. Term these control channel codewords. Each of these control channel codewords carries information about a corresponding shared channel codeword. Each control channel codeword indicates to the UE the transmission format that has been or will be used in transmission to the UE on a particular physical resource allocation. Within each of these control channel codewords are indications of modulation and channel coding rate (or equivalently transport block size/codeblock length). In the wireless communications art, modulation and coding rate/codeblock length are termed together as a modulation and coding rate set MCS. Assume for example that two bits are needed to indicate the modulation type allocated by the network to a UE, and five bits are needed to indicate the coding rate allocated by the network to that same UE in that same allocation. The MCS would then be seven bits long. For the case where there are two control channel codewords for a single allocation of network physical resources (e.g., one or more physical resource blocks allocated in a single network grant to one UE), each control channel codeword carries seven bits for MCS. Since the bit rate of the control channel should be kept as minimal as possible, it is desirable to minimize the overhead from these control channel codewords.
Also, the UE may transmit channel quality information (CQI) on an uplink control channel related to a possible DL transmission format with multiple shared channel codewords. In that case, the CQI reporting can be interpreted to consist of several UL control channel codewords, one for each of the DL shared channel codewords.